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document box distance KNN operator

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git-svn-id: http://svn.osgeo.org/postgis/trunk@7911 b70326c6-7e19-0410-871a-916f4a2858ee
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Regina Obe 2011-09-28 21:56:42 +00:00
parent 05a1752c44
commit 04eda6922a
1 changed files with 83 additions and 5 deletions
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doc/reference_operator.xml
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@ -1064,12 +1064,13 @@ select 'LINESTRING(0 0, 1 1)'::geometry ~= 'LINESTRING(0 1, 1 0)'::geometry as e
</refsection>
</refentry>
<refentry id="geometry_gist_boxdistance_2d">
<refentry id="geometry_distance_centroid">
<refnamediv>
<refname>&lt;-&gt;</refname>
<refpurpose>Returns the squared distance between two points. For point / point checks it's exact. For other geometry types
only the centroid of the bounding box is considered. Useful for doing distance ordering and nearest neighbor limits.</refpurpose>
<refpurpose>Returns the distance between two points. For point / point checks it's exact. For other geometry types
the distance between the bounding box centroids is returned. Useful for doing distance ordering and nearest neighbor limits
using KNN gist functionality.</refpurpose>
</refnamediv>
<refsynopsisdiv>
@ -1099,7 +1100,8 @@ select 'LINESTRING(0 0, 1 1)'::geometry ~= 'LINESTRING(0 1, 1 0)'::geometry as e
other geometries it returns squared distance from centroid of bounding box of geometries. Useful for doing nearest neighbor approximate distance ordering.</para>
<note><para>This operand will make use of any indexes that may be available on the
geometries.</para></note>
geometries. It is different from other operators taht use spatial indexes in that the spatial index is only used when the operator
is in the ORDER BY clause.</para></note>
<para>Availability: 2.0.0 only available for PostgreSQL 9.1+</para>
@ -1173,7 +1175,83 @@ Finally the hybrid:
</refsection>
<refsection>
<title>See Also</title>
<para><xref linkend="ST_DWithin" />, <xref linkend="ST_Distance" /></para>
<para><xref linkend="ST_DWithin" />, <xref linkend="ST_Distance" />, <xref linkend="geometry_distance_box" /></para>
</refsection>
</refentry>
<refentry id="geometry_distance_box">
<refnamediv>
<refname>&lt;#&gt;</refname>
<refpurpose>Returns the distance between two points. For point / point checks it's exact. For other geometry types
the distance between the bounding box centroids is returned. Useful for doing distance ordering and nearest neighbor limits
using KNN gist functionality.</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>double precision <function>&lt;#&gt;</function></funcdef>
<paramdef>
<type>geometry </type>
<parameter>A</parameter>
</paramdef>
<paramdef>
<type>geometry </type>
<parameter>B</parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsection>
<title>Description</title>
<para>The <varname>&lt;#&gt;</varname> KNN GIST operator returns distance between two bounding boxes read from the spatial index if available. Useful for doing nearest neighbor approximate distance ordering.</para>
<note><para>This operand will make use of any indexes that may be available on the
geometries. It is different from other operators that use spatial indexes in that the spatial index is only used when the operator
is in the ORDER BY clause.</para></note>
<para>Availability: 2.0.0 only available for PostgreSQL 9.1+</para>
</refsection>
<refsection>
<title>Examples</title>
<programlisting>
-- this takes 125 ms on 25,000 gist indexed street table
<![CDATA[SELECT *
FROM (
SELECT b.tlid, b.mtfcc, b.geom <#> d.geom As b_dist, ST_Distance(b.geom, d.geom) As act_dist
FROM bos_roads As b
CROSS JOIN (SELECT geom FROM bos_roads WHERE tlid = 85732029) As d
ORDER BY b.geom <#> d.geom, b.tlid
LIMIT 100) As foo
ORDER BY act_dist, tlid LIMIT 10;]]>
tlid | mtfcc | b_dist | act_dist
-----------+-------+------------------+------------------
85732027 | S1400 | 0 | 0
85732029 | S1400 | 0 | 0
85732031 | S1400 | 0 | 0
85734335 | S1400 | 0 | 0
85736037 | S1400 | 0 | 0
624683742 | S1400 | 0 | 128.528874268666
85719343 | S1400 | 260.839270432962 | 260.839270432962
85741826 | S1400 | 164.759294123275 | 260.839270432962
85732032 | S1400 | 277.75 | 311.830282365264
85735592 | S1400 | 222.25 | 311.830282365264
(10 rows)
</programlisting>
</refsection>
<refsection>
<title>See Also</title>
<para><xref linkend="ST_DWithin" />, <xref linkend="ST_Distance" />, <xref linkend="geometry_distance_centroid" /></para>
</refsection>
</refentry>